Species in areas with exceptionally high biodiversity (richspots), especially of endemic species (unique to that place), are consistent losers under climate change because they cannot disperse to more suitable climates. In contrast, introduced invasive species tend to be unaffected by climate change or benefit from it, and their expansion will further threaten the survival of native species and their habitats.
Without a reduction of greenhouse gas emissions, 20% of all species in these biodiversity richspots have a high risk of extinction. In especially isolated areas including islands and mountains, all the endemic species there are at risk of extinction. Endemic species were nearly 3 times more likely to go extinct with unchecked temperature increases than species that are widespread.
For a doubling of global warming, there is at least a ten-times increase in extinction risk. If global warming is kept to within 1.5 °C (it has already warmed by a global average of 1 °C, more in some places, less in others) then 2% of endemic species on land and sea have a high risk of extinction. At 2 °C global warming the proportions of species at high extinction risk rise to 4% and 13%. At >3 °C warming, 20% and 32% are at risk. Thus the impacts of climate change on biodiversity are not proportional to the amount of warming.
We found that if the planet heats by over 3°C then a third of endemic species living on land, and almost half of endemic species living in the sea, face extinction. On mountains, 84% of endemic animals and plants face extinction at these temperatures, while on islands that number rises to 100%. Overall, 92% of land-based endemic species and 95% of marine endemics face negative consequences, such as a reduction in numbers, at 3°C. Current policies put the world on track for around 3°C of heating.
Of endemic species, 34% and 46% in terrestrial and marine ecosystems, and 100% and 84% of island and mountain species were projected to face high extinction risk respectively. Marine species at most risk live in enclosed seas such as the Mediterranean, from where they can be trapped under global warming.
Our study did a systematic search of the literature regarding climate change effects on biodiversity in the “Global 200” ecoregions and other areas called “biodiversity hotspots”. The authors studied each paper and pooled their results into one giant spreadsheet for statistical analysis. In the paper, we called the areas “richspots” to avoid any confusion with the use of the term ‘hotspots’ for areas of high warming and high pollution. The effects studied were species richness and abundance, natural habitat quality and cover, physiological impacts on species, and risk of extinction.
The overwhelmingly consistent negative impacts of climate warming was a surprise. Some species may benefit from climate change by it making for a more suitable environment for them, and/or allowing them to expand their range. However, in these richspots all the effects were negative, including by climatic zone, environment (marine, freshwater, terrestrial), taxonomic group (with one exception for amphibia in a South American area), and geographic region. This seems to be because these areas have a high proportion of endemic species (meaning species that occur nowhere else). Were these species able to disperse across and live in adjacent areas then they would not be endemic. This means they are trapped in their present area and if the climate becomes less suitable for them directly, or for their food supply, they are at increased risk of extinction.
So what? Countries need to fulfil their promises to protect nature and use nature in an environmentally sustainable way, especially in these biodiversity richspots. Otherwise, even without climate change, there will be high extinctions of endemic species due to existing human impacts such as habitat loss, hunting and fishing. Without reducing greenhouse gas emissions globally, climate change driven extinctions will happen even within protected richspots. Interventions to protect species through captive breeding and relocation would be expensive and uncertain.
Some media commentary
Jamie Morton. 2021. Covering Climate Now: Warming will hit endemic species hardest. New Zealand Herald.
AFP. 2021. Diversity on ocean floor near equator may disappear, researchers warn. Global Times.
The Guardian created a short video on this paper for Tik Tok https://www.tiktok.com/@guardian/video/7026766371455257861